The present invention relates to improvements in the cover for a valve rocker compartment of internal combustion engines, in general. As is well known, in internal combustion engines the rockers which open and close the intake and exhaust valves are located on the cylinder head in a compartment closed by a cover, which is fixed in a sealed manner onto the cylinder head. The space between the cylinder head and cover is connected to the engine crankcase by way of an aperture through which the rocker operating rods pass, so that the vapor generated when the lubricating oil contained in the crankcase increases in temperature seeps into the compartment to place it under a slight pressure.
To prevent overpressure in the compartment containing the valve rockers, its cover either comprises an outwardly directed vent or, to prevent pollution, is connected by a tube to the air filter.
Whether this connection is made upstream or downstream of the filter cartridge, it creates difficulties. In this respect, in the first case said vapor causes early clogging of the filter elements in the air filter. In the second case, if a large negative pressure arises in the intake manifold due to clogging of the air filter, it is transmitted to the compartment containing the value rockers with the result that the lubricating oil can be drawn up from the crankcase and sucked into the engine cylinder (or cylinders), thus feeding the combustion and progressively drying the sump, resulting in danger to persons and damage to the engine.
The main object of the present invention is to provide an arrangement which obviates the aforesaid problems within the context of a simple, reliable and low-cost construction.
According to the present invention, the proposed cover comprises a duct system which extends from the valve spring retainer to the engine intake manifold and contains a valving member arranged to close said duct system only when the vacuum in the manifold reaches undesirable values for any reason, for example because of clogging of the air filter.
This can be achieved for example by elastic means having a predetermined preload i.e. able to retain the valving member in its open position with a force which is able to oppose the suction action due to the usual range of vacuum in the manifold.
In other words, the valving member is insensitive to the vacuum which is produced by normal air intake conditions, whereas said valving member closes said duct system when the vacuum increases and approaches the limiting value which would result in oil being drawn up from the engine crankcase.
These and further merits and characteristics of the present invention will be more apparent from the detailed description give hereinafter with reference to the accompanying figures which illustrate a preferred embodiment thereof by way of non-limiting example only.